The expansion of variable renewable generation is increasing the need for operational flexibility in the Brazilian power system. This study examines the regulatory evolution of demand response (DR) in Brazil and identifies the conditions required for its integration into the National Interconnected System as a structured flexibility resource. A qualitative document-based analysis of scientific, technical, regulatory, and institutional sources is conducted. The assessment covers resource adequacy, short-term balancing, congestion management, renewable-energy absorption, curtailment mitigation, and prospective offshore wind integration. The Brazilian framework has evolved from pilot and emergency-oriented initiatives towards structural and availability-based arrangements. Further consolidation requires differentiated products defined by response time, duration, location, availability, and delivery reliability, supported by robust baseline methodologies, measurement and verification, telemetry, performance assessment, aggregation, and coordinated settlement. Demand-side flexibility can support renewable integration through load reduction, load shifting, and controlled consumption increases. Its effectiveness in mitigating curtailment, however, depends on the cause and location of the operational constraint. DR should therefore complement hydroelectric coordination, transmission expansion, storage, forecasting, and distributed energy resources within a diversified flexibility portfolio.